This invention relates to the separation and recovery of valuable metals from metal and non-metal composite materials such as printed wiring boards (in particular, their rejects and scraps) that are extensively used in the field of industrial electronics. More specifically, the invention relates to a method that comprises grinding such composite materials under specified conditions, separating spherical metal particles from non-spherical resins and other non-metal components by shape separation, and recovering either the metal particles or the resins or the like or both as valuables to be recycled.
Printed wiring boards using epoxy-glass substrates are produced in large quantities in the electronic industry and, accordingly, lots of scraps and rejects occur in their production line. Such scraps and rejects of printed wiring boards are composed of glass fibers and plastics as the substrate materials and metals such as copper, nickel, gold and silver in the circuit patterns. Because of this mixed nature, scrap and rejected printed wiring boards are not only difficult to grind but also the heat-setting property of the plastics makes the remelting approach impractical. Therefore, the scraps and rejects of printed wiring boards are in most cases disposed of in the form of a landfill without being recycled.
If the printed wiring board to be treated has patterned layers of valuable metals such as copper and nickel applied in thicknesses greater than 30 .mu.m or if it has thinner layers of more expensive noble metals such as gold, silver and palladium, only the metals can be recovered by an existing technology that involves surface etching. However, this technology requires wastewater treatment facilities to recover valuable metals and, furthermore, the substrates that remain after their recovery have to be managed either by land disposal in the form of a landfill or by incineration. In the former case, the resins of which the substrates are formed will not corrode in the soil and in the latter case noxious gases such as hydrogen chloride, hydrogen bromide and dioxin will evolve to increase the management cost. The technology has no effective means to provide a complete solution to these problems
As disclosed in Unexamined Published Japanese Patent Application (kokai) Hei 2-218486, entitled "A method of recovering metallic copper from the shredder dust or scrap of printed circuit boards", a technique has been proposed that comprises the steps of shredding a scrap composite material with a shearing machine, reducing its size with a grinder, and separating out the metal by specific density on a suitable device such as a vibrating table. However, no complete separation can be achieved between the metal and the resins, etc.
In commonly assigned Unexamined Published Japanese Patent Application (kokai) Hei 6-170276, entitled "A method of separating and recovering valuables from composite materials", the applicant proposed a method comprising the steps of breaking a composite material of interest into pieces by a suitable means such as a shearing machine, grinding the pieces by a suitable means such as a hammer mill to form a mixed powder consisting of metal and non-metal particles, and passing the mixed powder through either an eddy-current separator or an electrostatic separator or both so that the metal particles are separated from the non-metal particles. However, later studies have shown that this method is still imperfect in that the recovered metal particles contain a small amount of the non-metal particles.
The present invention has been accomplished under these circumstances and has as an object providing a method in which a composite material is ground within a specified range of peripheral speed and in which the fine particles thus obtained are passed through a specified separator, whereby the valuable metal component is separated efficiently from the non-metal component consisting of resins, glass fivers, etc.